The present invention is generally directed to processes for the preparation of toner compositions and processes for using the toner composition in ink jet printing applications. More specifically, the present invention relates to processes which provide sterically and/or electrostatically stabilized in situ toner compositions and stabilized pigment particles which are suitable for use in electrophotographic imaging and ink jet printing methods. The present invention also relates to polymerization processes for preparing stabilized resin particle products that possess narrow molecular weight distributions or polydispersity properties and narrow particle size distributions, and which polymerization processes proceed with high monomer to polymer conversion. In particular, the present invention relates, in embodiments, to polymerization processes which directly yield stabilized resin particles having resin number average molecular weights (M.sub.n) equal to or above about 2,000 to about 500,000 and having a polydispersity ratio of the weight average molecular weight (M.sub.w) to the number average molecular weight (M.sub.n) of from about 1.0 to about 2.0, and preferably about 1.1 to about 1.5. As used herein, the term "stabilized" refers to known electrostatic and/or steric solid-liquid or colloidal dispersion phenomena. The stabilized resin particles and stabilized pigment particles that are formed by in situ monomer polymerization reactions and pigment coupling reactions, respectively, in embodiments, may be used directly in selected liquid based imaging applications without the need for further processing steps, such as isolation, purification, classification, and the like. In other embodiments, the present invention provides processes for preparing stabilized pigment particles, which stabilization processes provide an alternative approach to conventional methods for stabilizing typically unstable pigment particle dispersions for use in, for example, aqueous and non-aqueous ink jet ink formulations. The present invention also provides, in embodiments, a pseudoliving polymerization process that enables the direct preparation of narrow polydispersity homopolymeric and copolymeric "reactive emulsifiers" which may be used to prepare stabilized resin particles directly from monomers; and stabilized pigment particles. In embodiments, first formed intermediate polymers, alternatively referred to as stabilizer compounds or reactive emulsifiers, are of the formula (I-A-B-)-SFR where l is a free radical initiator molecular fragment, A is a polymeric segment and B is a polymeric segment and which segments can be the same or different in composition and physical properties, and SFR represents a covalently bonded and thermally labile latent stable free radical functional group. The intermediate polymers may be optionally isolated and stored indefinitely at ambient temperature or reacted directly, or in situ, with additional monomer or monomers to form stabilized resin or pigment particles. The processes of the present invention can, in embodiments, use known free radical initiators in combination with, for example, an oxygenated stable free radical agent, and a free radical reactive, polymerizable, monomer or monomers to afford stabilized, narrow polydispersity, homo- and copolymeric resin particles. The aforementioned resin particle formation and stabilization processes can optionally incorporate a colorant into the reaction mixture before, during, or after polymerization to provide particle coloration capability. In an alternative embodiment, the aforementioned stabilized pigment particles may be added to the aforementioned stabilized resin particle formation process to provide enhanced pigment dispersion and stability properties to the resulting pigmented resin particles or toner particles. Enhanced pigment dispersion and stability in toner particles in turn imparts desirable image quality characteristics to electrophotographic and liquid ink impressions and transparencies, particularly for color images, for example, high fidelity color reproduction and transparency projection efficiencies.
Conventional free radical polymerization processes that have been used to polymerize unsaturated or olefinic monomers inherently provide broad polydispersity resin products or require that sophisticated processing conditions and materials handling protocols be employed to control, to some extent, the polydispersity properties of the resin products, for example, carefully controlling reactor temperature profiles or monomer addition rates. The resin products prepared from the aforementioned conventional free radical polymerization processes generally require post reaction processing, such as isolation and purification, before the resin product is in a suitable condition for formulating with other components, such as colorants and charging additives, for the purpose of preparing dry or liquid toner particle formulations.
Many known polymerization processes used for the synthesis of narrow polydispersity resins, such as anionic, cationic, and group transfer polymerization processes, are severely limited by the need for anhydrous reaction conditions and monomers which do not contain protic or reactive functional groups, for example, hydroxy (OH) carboxy (CO.sub.2 H), amino (NH), and the like. As a consequence, these processes are not readily applicable to the polymerizaton of functionalized monomers since these monomer materials tend to be chemically reactive or hydroscopic whereby any associated water may readily destroy the polymerization initiator component, for example, the hydrolysis or protonation of organolithium reagents that are used in anionic polymerization processes, or in other ways cause the polymerization to fail entirely or to be industrially inefficient.
It is generally accepted that known anionic and cationic polymerization processes used for the preparation of narrow polydispersity resins, diblock and multiblock polymers are not believed possible in aqueous or protic solvent containing polymerization media, or in the presence of aforementioned protonic or reactive functional groups. Control of the polydispersity and blockedness of the resin enables control of toner melt rheology properties such as T.sub.g and hot offset temperature, reference, for example, the aforementioned U.S. Pat. No. 5,312,704.
Of the known polymerization processes a preferred way to prepare polymers or copolymers having a narrow molecular weight distribution or polydispersity is by anionic processes. The use and availability of resins having narrow polydispersities in industrial applications is limited because anionic polymerization processes must be performed in the absence of atmospheric oxygen and moisture, require difficult to handle and hazardous initiator reagents, and consequently such polymerization processes are generally limited to small batch reactors. In addition, the monomers and solvents that are used must be of high purity and anhydrous thereby rendering the anionic process more expensive and tedious than alternatives which do not have these requirements. Thus, anionic polymerization processes are difficult, costly and dangerous. It is desirable to have free radical polymerization process that provides narrow molecular weight distribution stabilized resin particles that overcomes the shortcomings and disadvantages of the aforementioned anionic and related polymerization processes.
Similarly, group transfer polymerization (GTP) processes have limitations and disadvantages, such as anhydrous reaction conditions and expensive reagents, which disadvantage GTP processes for large scale industrial applications.
Free radical polymerization processes are generally chemically less sensitive than anionic processes to impurities in the monomers or solvents typically used and are substantially or completely insensitive to water. There has been a long felt need for an economical free radical polymerization process which is suitable for directly preparing narrow polydispersity resins, stabilized resin and toner particles, and stabilized pigment particles by free radical reaction processes.
Copolymers prepared by conventional free radical polymerization processes inherently have broad molecular weight distributions or polydispersities, generally greater than about four. One reason is that most free radical initiators selected have half lives that are relatively long, from several minutes to many hours, and thus the polymeric chains are not all initiated at the same time and which initiators provide growing chains of various lengths at any time during the polymerization process. Another reason is that the propagating chains in a free radical process can react with each other in processes known as coupling and disproportionation, both of which are chain terminating and polydispersity broadening reaction processes. In doing so, chains of varying lengths are terminated at different times during the reaction process which results in resins comprised of polymeric chains which vary widely in length from very small to very large and thus have broad polydispersities. If a free radical polymerization process is to be enabled for producing narrow molecular weight distributions, then all polymer chains must be initiated at about the same time and premature termination by coupling or disproportionation processes must be avoided or eliminated.
Contemporary environmental issues and pollution concerns are prompting greater use of certain biodegradable polymers, among these are water soluble polymers as described by F. Lo, J. Petchonka, J. Hanly, Chem. Eng. Prog., Jul., 1993, p. 55-58, the disclosure of which is incorporated by reference herein in its entirety. In embodiments of the present invention are provided water soluble and biodegradable polymeric resins.
Conventional processes for preparing sterically and/or electrostatically stabilized resin or sterically stabilized pigment particles are confounded by the aforementioned problems of anionic and cationic processes which require scrupulously dry solvents and reactants, and monomer compounds without reactive functionality. Other stabilization processes known in the art use oxygenated polymeric compounds, such as polysaccarides, as macromolecular steric stabilizers. These stabilizer compounds are either physi-sorbea or physically embedded into the surface of the resin or toner particles. Covalent attachment of these and other stabilizer compounds to the particle surface has proven to be a difficult and expensive proposition. Oxygenated polymeric steric stabilizer compounds typically render the resulting particles humidity sensitive thereby making the resultant stabilized dry toner particles and developer compositions also humidity sensitive.
The following patents are of interest, the disclosures of which are incorporated by reference herein in their entirety:
In U.S. Pat. No. 5,728,239, to Hoxmeier, issued Jan. 11, 1994, there is disclosed a process for producing a coupled polymer by anionically polymerizing monomers selected from the group consisting of a vinyl aromatic hydrocarbon, a conjugated diene or both with an organo alkali metal compound to produce living polymers. The living polymers are then contacted with a fullerene which form a multiply coupled polymer-fullerene adduct. The coupled polymer-fullerene adduct has a novel composition and novel characteristics.
U.S. Pat. No. 4,597,794, to Ohta et al., issued Jul. 1, 1986, discloses an ink-jet recording process which comprises forming droplets of an ink and recording on an image receiving material by using the droplets, said ink is prepared by dispersing fine particles of pigment in an aqueous dispersion medium containing polymer having both a hydrophilic and a hydrophobic construction portion. An average particle size (D micron) of the pigment and an average molecular weight of the polymer satisfy the relationship represented by the equation D.times.5.times.10.sup.2 .ltoreq.W, and the ratio of molecular weight of the pigment to average molecular weight of the polymer is a value in the range from 1:2 to 1:150.
U.S. Pat. No. 4,846,893, to Akasaki, issued Jul. 11, 1989, discloses a process for producing a surface treated pigment wherein pigment particles are dispersed in a solution of a water soluble high polymer having radical generation sites to absorb the water soluble high polymer on the surfaces of the pigment particles, adding vinyl monomer to the resulting aqueous liquid dispersion of the pigment particles subjected to the adsorption treatment and polymerizing in the presence of a polymerization initiator, if desired, to form a polymer layer on the surfaces of the pigment particles. Formation of the white polymer particles composed only of polymer can be prevented and dispersion stability can be improved.
U.S. Pat. No. 4,476,210 to Croucher et al., issued Oct. 9, 1984, discloses a stable colored liquid developer and method for making such are described wherein an improved optical density resulting from a colored dye being imbibed into a thermoplastic resin core occurs. In particular, the liquid developer comprises a marking particle dispersed in an aliphatic dispersion medium, the marking particle comprises a thermoplastic resin core having an amphipathic block or graft copolymeric steric stabilizer irreversibly chemically or physically anchored to the thermoplastic resin core with the dye being imbibed in the resin core and being soluble therein and insoluble in the dispersion medium. The stable colored liquid developer is preferably made by first preparing a graft or block copolymer amphipathic steric stabilizer, anchoring said stabilizer to a thermoplastic resin core, and to the aliphatic dispersion of said particle adding a solution of a dye dissolved in a polar solvent, preferrably methanol, the dye being soluble in the thermoplastic resin core to enable it to be imbibed therein and substantially insoluble in the dispersion medium.
U.S. Pat. No. 5,281,261, to Lin, issued Jan. 25, 1994, discloses an ink composition comprising an aqueous liquid vehicle and pigment particles having attached to the surfaces thereof a polymerized vinyl aromatic salt. In one embodiment, the polymeric vinyl aromatic salt is chemically grafted to the surfaces of the pigment particles; in another embodiment, the polymeric vinyl aromatic salt is adsorbed onto the surfaces of the pigment particles. Preferably, the modified pigment particles have an average particle diameter of less than about 1 micron. The ink composition is suitable for applications such as ink jet printing processes, particularly thermal ink jet printing processes. Images generated with ink compositions of the disclosed invention are sharp, waterfast, lightfast, and of high optical density, exhibiting no feathering, and can be electrically conductive.
U.S. Pat. No. 4,530,961 to Nguyen et al., issued Jul. 23, 1985, discloses an aqueous dispersion of carbon black grafted with hydrophilic monomers such as alkali or ammonium carboxylate bearing polymers. The dispersion has a viscosity of about 2 to about 30 cP for a carbon black content of about 1 to 15 percent by weight.
U.S. Pat. No. 4,314,931 to Hoffend et al., issued Feb. 9, 1982, discloses a process for substantially eliminating polymerization inhibition in a pigment containing dispersion polymerizaton reaction, which comprises grafting polymer molecules onto the pigment used in the polymerizaton reaction, whereby there results a polymerized product which contains essentially no monomer material.
U.S. Pat. 4,581,429, to Solomon et al., issued Apr. 8, 1986, discloses a free radical pseudoliving polymerization process which controls the growth of polymer chains to produce short chain or oligomeric homopolymers and copolymers including block and graft copolymers. The process employs an initiator having the formula (in part)=N-O-X, where X is a free radical species capable of polymerizing unsaturated monomers. The working examples of this patent illustrate low monomer to polymer conversion, and in some instances, the polydispersity is reported as 1.15, see Example 34. All of the polymerization Examples of this patent are to be reviewed with respect to the present invention.
U.S. Pat. 5,059,657 to Druliner et al., issued Oct. 22, 1991, discloses a polymerization process for acrylic and maleimide monomers by contacting the monomers with a diazotate, cyanate or hyponitrite, and N-chlorosuccinimide, N-bromosuccinimide or a diazonium salt. The polymer produced can initiate further polymerization, including use in block copolymer formation.
The following references are also of interest: U.S. Pat. Nos. 2,913,429; 2,971,935; 3,306,871; 3,682,875; 3,879,360; 3,954,722; 4,201,848; 4,524,199; 4,542,182; 4,581,429; 4,652,508; 4,777,230; 4,816,370; 5,059,657; 5,173,551; 5,191,008; 5,191,009; 5,194,496; 5,216,096; 5,247,024; 5,268,437; 4,546,160; and 4,736,004; U.K. Patent 895,033; and German Patent 1,051,501.
Other references cited in an international search report for the aforementioned U.S. Pat. No. 5,322,912 are: J. Am. Chem. Soc., 1983, 5706-5708; Macromol., 1987, 1473-1488; Macromol., 1991, 6572-6577; U.S. Pat. No. 4,628,019 to Suematsu et al., issued Aug. 10, 1986; U.S. Pat. No. 3,947,078 to Crystal, issued Aug. 10, 1976; and U.S. Pat. No. 3,965,021 to Clemens et al., issued Jun. 22, 1976.
In free radical polymerization reaction processes of the prior art, various significant problems exist, for example difficulties in predicting or controlling both the polydispersity and modality of the polymers produced. These processes generally produce polymers with high weight average molecular weights (M.sub.w) and low number average molecular weights (M.sub.n) resulting in broad polydispersities or low molecular weight (M.sub.n) and in some instances low conversion. The Solomon patent, reference the examples, see especially Examples 34A and 34B, illustrates narrow polydispersities of the example 1.15, however the conversion is low, less than about 22% for example, and this process utilizes a reaction adduct or product of a carbon centered free radical and a stable free radical to initiate polymerization. Further, generally the free radical polymerization processes of the prior art are prone to generating excessive quantities of heat since the polymerization reaction is exothermic. As the viscosity of the reaction medium increases, dissipation of heat becomes more difficult. This is referred to as the Trommsdorff effect as discussed and illustrated in Principles of Polymerization, G. Odian, 2nd Ed., Wiley-Interscience, N.Y., 1981, page 272, the disclosure of which is entirely incorporated herein by reference. This is particularly the situation for reactions with high concentrations of soluble monomer, for example greater than 30 to 50 percent by weight soluble monomer, which are conducted in large scale reactors with limited surface area and limited heat dissipation capacity. Moreover, the exothermic nature of free radical polymerization processes is often a limitation that severely restricts the concentration of reactants or the reactor size upon scale up.
Further, gel body formation in conventional free radical polymerization processes may result in a broad molecular weight distributions and/or difficulties encountered during filtering, drying, dissolving, and manipulating the product resin, particularly for highly concentrated reactions.
These and other disadvantages are avoided, or minimized with the free radical polymerization, stabilization, and derivatization processes of the present invention.
Practitioners in the art have long sought an inexpensive, efficient and environmentally efficacious means for preparing stabilized resin and pigment particles, and which stabilized particles are suitable for use in preparing dry and liquid developer compositions and imaging processes.
Thus, there remains a need for polymerization processes for the preparation of narrow polydispersity reactive emulsifier compounds and polymeric resins, and for derivatization processes for preparing stabilized resin and pigment particles by economical and scalable free radical polymerization techniques and which polymers and particles retain many or all of their desirable physical properties, for example, hardness, low gel content, processability, clarity, high gloss durability, and the like, while avoiding problems such as gel formation, exotherms, volume limited and multi-stage reaction systems, purification, performance properties of the polymer resin products, and the like, associated with prior art free radical polymerization and particle stabilization methodologies.
The present invention provides intermediate product polymers containing a latent, thermally reactive, functional group on at least one end of the polymer molecule which are subsequently used in reactions to prepare resin particles with desired resin architectures, particle size, and colloidal stability properties. The present invention, in embodiments, provides polymerization processes that enable control of resin molecular weight, weight distribution, modality and homogenity of the products, and the like properties.
The present invention is also directed to pseudoliving polymerization processes which permit the economic preparation of narrow polydispersity resins with low, intermediate, or high molecular weights. The low molecular weight resins can be prepared without a chain transfer agent or molecular weight modifier which provides several advantages over conventional chain transfer mediated polymerization processes.
The polymerization processes, thermoplastic resin products, and stabilized resin and pigment particle formulations of the present invention are useful in many applications, for example, specialty applications including toner, liquid immersion development ink resin particles, and ink jet inks and performance additives for electrophotographic and non-electrophotographic imaging processes.